The invention relates to a bus system with a plurality of stations which are coupled to one another via a system of conductors and each of which includes a transceiver and a control unit.
Systems of this kind are used mainly in vehicles. Vehicles must remain operational also after having been parked for weeks and hence are subject to severe quiescent current conditions. Contemporary Vehicles contain increasing amounts of entertainment, comfort and communication electronics which are activated at least from time to time, also when the vehicle is parked, in order to execute monitoring functions or to collect information in advance for the driver, for example traffic messages.
DE 197 04 862 describes a system in which a suitable choice of signal and wake-up levels enables the formation of a sub-system between a number of stations in a bus system; some of the stations then communicate with one another while the other stations of the bus system are in the quiescent state. The complete system is awakened by means of a given wake-up level which is clearly distinct from the normal signal levels, i.e. all stations then change over from the quiescent state to the normal operating state. Subsequently, the participants in the sub-system are identified and the stations that are not concerned return to the quiescent state.
This solution has the drawback that, as before, all stations assume the normal operating state at least once at the beginning of each communication phase of a sub-system. Consequently, the power consumption is not significantly reduced, particularly if the communication is frequent and short. Because the non-participating stations are in the quiescent state, the transceiver does not prepare the necessary quiescent voltage level, so that the transmission properties of the overall system are affected.
It is an object of the invention to realize a sub-network mode of operation in which the power consumption is reduced and which decouples the functionality of the transmission system from the functionality of the microcontroller.
This object is achieved according to the invention in that at least one station is arranged to switch over from a quiescent state to a standby state in response to the reception of a first wake-up signal, and that selected stations are switched to a normal operating state upon reception of a second wake-up signal for the selection of stations.
Bus systems include a plurality of stations, the individual stations being capable of executing different functions. However, the execution of sub-functions does not require complete functionality of all the stations connected to the bus system. The stations are connected to one another via a system of conductors and include a control unit in addition to a transceiver.
In order to realize a sub-system, all stations connected to the bus systems are first switched from a quiescent state to a standby state by means of a first wake-up signal or first wake-up request transmitted via the system of conductors. In the quiescent mode the stations are currentless and their power consumption is extremely low. The stations include a receiver which is accommodated in the transceiver and has all features necessary to receive a first wake-up signal. After reception of the first wake-up signal, the stations are switched to a standby state. The power consumption in the standby state is slightly higher than that in the quiescent state, but the station performs all duties that have to be done at least so as to enable unrestricted communication by other stations. The power consumption, however, is far less than that in the normal operating state. Moreover, in this standby state the station is capable of unambiguously detecting a second wake-up signal or wake-up request intended for this station. After identification of the second wake-up signal, the control unit sets the selected station to the normal operating state. Because usually several individual stations communicate with one another in order to execute sub-functions, the second wake-up signal is transmitted to all stations required for the execution of a sub-function. Due to this second wake-up signal and the switching over of the selected stations to the normal operating state a sub-system is established for the execution of a sub-function. Stations that are not required for the execution of the relevant sub-function remain in the standby state.
The control unit of the station includes a microcontroller and a protocol controller. The microcontroller executes application-specific tasks and the protocol controller is responsible for the execution of a specified transmission protocol.
It has been found that the transceiver is advantageously arranged to receive the first wake-up signal as well as the second wake-up signal. For the reception of the first wake-up signal the transceiver includes a receiver which is also capable of detecting a first wake-up request in the quiescent state; after the reception of this first wake-up signal the station is switched from the quiescent state to the standby state by the transceiver. In this standby state the transceiver can recognize a second wake-up signal which is applied directly to the relevant station so as to select this station. It is only when the transceiver has recognized that its station has been selected that it informs the control unit which then switches the complete station to its normal operating state. The other stations, not being required for the sub-function, remain in the standby state. When the communication between the stations in the normal operating state is terminated, these stations are switched to the standby state by their respective control unit. The transceiver keeps the stations which just were in the normal operating state and the stations which were also in the standby state during the communication in the standby state until, for example no communication has taken place on the entire bus system for a predetermined period of time. This results in an optimum saving of power. The decoupling of the responsibilities between transceiver and control unit at the same time enhances the availability of the overall bus system. Stations in which faults occur in the control unit because of, for example software errors, thus cannot influence the communication and the availability of the overall bus system because, even in the case of incorrect operation of the control unit, the transceiver performs all duties required to enable unimpeded communication by all other stations.
In a further embodiment of the invention the first wake-up signal is generated, for example by a locally wakened station. Because the individual stations execute different functions, they also have different components. For example, a station could be locally wakened via an internal clock so as to measure the ambient temperatures for the purpose of preheating of the vehicle. Moreover, for the reception of traffic messages a station could be locally wakened by a received traffic radio transmission symbol in order to collect traffic messages which are then presented to the driver in a route-specific fashion when the drive commences.
When a station is wakened by such external influence, it is switched directly to its normal operating state by its control unit. In this state the station can transmit the first wake-up signal to all stations via the bus system. In response thereto all stations are set to their standby state by their transceivers. The locally wakened station then applies second wake-up signals to all stations required for the current sub-function to be executed. This local wake-up function and the autonomous dispatch of wake-up signals enable a decentralized configuration of the bus system for the execution of sub-functions and for the formation of a sub-system, so that a significant amount of energy is saved again.
In a preferred further embodiment of the bus system the station is arranged so as to be in a quiescent state with switched-on regulated voltage supply. Stations may be in this quiescent state with switched-on regulated voltage supply when they execute local sub-functions or await the reception of data. In such a case the transceiver switches the station to the standby state with switched-on regulated voltage supply upon reception of the first wake-up signal. After reception of the second wake-up signal the transceiver triggers a warm start in that it applies an interrupt to the control unit. The control unit switches the station to the normal operating state.
In order to achieve a further reduction of the power consumption, stations are arranged to operate in a quiescent state with switched-off regulated voltage supply. To this end, the transceiver of each station keeps a receiver ready which operates with a non-regulated voltage. This receiver is arranged to receive only the first wake-up signal or a local wake-up signal which is initiated by a switch or a control signal. After the reception of such a wake-up signal, the transceiver switches the station to the standby state with switched-off regulated voltage supply. The station then operates with a non-regulated voltage. When the station is then selected by the second wake-up signal, the transceiver switches on the regulated voltage supply, via a control signal, and hence switches the station to the normal operating state. This distinction enables a further saving of power.
Furthermore, the object of the invention is also achieved by a station in a bus system with a transceiver and a control unit in that the transceiver is arranged to switch over the station from a quiescent state to a standby state after the reception of a first wake-up signal, and that, after reception of a second wake-up signal whereby the station is selected, the station is switched to a normal operating state by the control unit.